Conventionally, vinyl chloride resins (PVC) have been extensively used in various applications such as automobile interior materials and sheets for construction. In particular, automobile interior sheets used as a skin layer of instrument panels, door trims, etc., have been made of soft polyvinyl chloride or a blended mixture of the soft polyvinyl chloride with other resins, or a laminate obtained by successively laminating a polyvinyl chloride layer whose surface is embossed into a leather-like pattern and a foam layer, and further, if required, a resin base layer.
However, the use of the vinyl chloride resins tend to cause various problems concerning reduction in weight of automobile parts, recyclability, needs of solving environmental problems such as easy-incineration property, heat resistance, cold resistance, anti-aging property, light resistance, odor and appearance with cheap feeling.
As the materials which are free from the above problems, there are known olefin-based thermoplastic elastomer compositions comprising a blended mixture comprising an ethylene-propylene-non-conjugated diene copolymer rubber and polypropylene in which a rubber component thereof is partially or completely dynamically crosslinked (hereinafter occasionally referred to merely as “TPO”). The above thermoplastic elastomer compositions are expected to provide useful alternative materials for vinyl chloride resins, and have been recently put into practice. As the TPO, for example, in Japanese Patent Application Laid-open (KOKAI) No. 6-1888, there is described a sheet-like molded product including an elastomer layer comprising a composition containing an olefin-based copolymer rubber, an olefin-based copolymer and a crystalline paraffin. In addition, in Japanese Patent No. 1658357, there has been proposed a laminate including a surface-embossed thermoplastic elastomer layer comprising a blended mixture of crosslinked TPO and an olefin-based resin, and a foam layer.
However, when the TPO is extrusion-molded into a sheet, a large amount of deposit, i.e., so-called gum, tends to be attached onto an outlet of an extrusion die or peripheral portions thereof, resulting in contaminated surface of the resultant molded product. Therefore, it has been required to stop operation of the extruder for cleaning the contaminated portions to remove deposit or gum therefrom, thereby causing problems such as deterioration in productivity. Thus, the TPO has problems on extrusion-moldability.
In addition, the resultant sheet tends to be deteriorated in scratch resistance and, therefore, becomes unusable in some applications. On the other hand, when the amount of resin components blended in the TPO is increased to enhance a scratch resistance thereof, the resultant composition has a high hardness and, therefore, fails to exhibit a desired soft feeling. To solve these problems, in Japanese Patent No. 2533147, there is described a laminate including a polyolefin-based thermoplastic elastomer layer, a primer layer having a specific composition and a top coat layer, and having excellent surface properties. However, such a laminate using the conventional TPO as a base material tends to be still unsatisfactory in scratch resistance even when any coating layer is provided thereon. Further, upon the extrusion molding, a large amount of deposit (gum) is attached onto an outlet of an extrusion die and peripheral portions thereof, resulting in contaminated surface of the resultant molded product. Therefore, it has also been required to stop operation of the extruder for cleaning the contaminated portions to remove deposit or gum therefrom, resulting in problems such as deterioration in productivity. In addition, when a mineral oil-based softening agent is blended in the resin composition to improve a softness thereof, the surface of the obtained molded product tends to become sticky owing to bleeding-out of the softening agent, so that the molded product might be unusable in some conditions or applications.
Further, when a sheet-like laminate using the conventional TPO as a base material is formed into a desired shape by ordinary secondary processing methods such as vacuum forming, pressure forming and stamping, the resultant products, especially those having a large drawing ratio, tend to suffer from problems such as occurrence of rupture and extremely small thickness due to lack of spreadability. Also, interior skin materials for instrument panels, door trims, etc., tend to be frequently provided on the surface thereof with emboss (embossed pattern) to attain a leather-like feeling or an anti-reflection property. When such sheet materials previously formed on the surface thereof with emboss (embossed pattern) are subjected to secondary processing such as vacuum forming, the resultant product tends to suffer from debossing (such a phenomenon that the depth of emboss (embossed pattern) is reduced), namely tends to undergo problems concerning retention of emboss (embossed pattern). To avoid the debossing, there has been proposed the method of conducting the vacuum forming process using a female metal die provided with emboss (embossed pattern). However, the above method has such a problem that the depth of emboss formed on the molded product is still insufficient as compared to that provided in the metal die.
On the other hand, it has been considered and attempted to use a styrene-based thermoplastic elastomer instead of the TPO. As such a styrene-based thermoplastic elastomer, there is known the composition comprising a hydrogenated derivative of a vinyl aromatic compound-conjugated diene compound block copolymer in combination with a mineral oil-based softening agent for rubbers, a propylene-based polymer and an inorganic filler, as described, for example, in Japanese Patent Application Laid-open (KOKAI) No. 58-206644. The styrene-based thermoplastic elastomer composition is excellent in softness, rubber elasticity and strength as well as moldability and, therefore, can be formed into products having a complicated shape by injection molding method, extrusion molding method, etc. However, when the styrene-based thermoplastic elastomer composition is formed into a sheet-like product by calendering method, it may be extremely difficult to form the composition into a sheet because of high stickiness thereof to calender rolls. Such an undesired phenomenon tends to be more remarkably caused with increase in amount of the softening agent blended, more specifically, when the mineral oil-based softening agent for rubbers is blended in an amount of not less than about 10 parts by weight based on 100 parts of a total amount of a styrene-based rubber and a polypropylene resin. However, the above blending weight ratio of the softening agent is a preferred range for the styrene-based thermoplastic elastomer composition comprising the above components. Therefore, it has been demanded to solve these problems without varying the preferred blending ratio.
Also, as materials used for calendering, there are known olefin-based thermoplastic elastomers prepared by blending an ethylene-based polymer resin and a higher fatty acid amide in an olefin-based copolymer rubber and a polypropylene-based polymer resin, as described, for example, in Japanese Patent No. 2985622. However, sheets obtained by calendering these materials tend to be deteriorated in scratch resistance and oil resistance.
The present invention has been accomplished in view of the above problems. A first object of the present invention is to provide a sheet comprising a thermoplastic elastomer having not only an excellent extrusion moldability but also excellent scratch resistance and soft feeling.
A second object of the present invention is to provide a laminate which is excellent in not only scratch resistance, oil resistance and soft feeling but also uniform spreadability and retention of emboss (embossed pattern).
A third object of the present invention is to provide a laminate which is excellent in not only scratch resistance, oil resistance and soft feeling but also uniform spreadability and retention of emboss (embossed pattern).
A fourth object of the present invention is to provide a laminate having excellent scratch resistance, oil resistance and soft feeling as well as good touch feeling which is free from gum formation and bleeding-out of softening agents.
A fifth object of the present invention is to provide a thermoplastic elastomer skin sheet that is free from gum formation upon molding, and excellent in scratch resistance, oil resistance and vacuum-forming property.
A sixth object of the present invention is to provide a thermoplastic elastomer composition having excellent oil resistance, scratch resistance and mechanical properties as well as a good appearance without bleeding-out which is suitable for calendering.